(Pure) Heroin is actually one of the least harmful drugs, physiologically speaking, provided it is taken under sterile conditions. Unlike cocaine or crystal meth, heroin does not permanently damage the stuctures of your brain or organs. The only physical problems associated with long-term heroin use are constipation and impaired libido/sexual functioning, as well as amenhorrea in women. The much-hyped dangers of heroin use (infection, HIV, death etc) are actually related more to the way it is often taken, ie with dirty needles etc. than to the use of heroin in itself. Of course, there is also the fact that heroin is extremely addictive, both physically and mentally. But if you are willing to put up with the constipation and low sex drive, and you can somehow obtain pure heroin (eg it's prescribed to terminally ill patients and even some addicts in England), it's actually one of the least "evil" drugs you can do as far as harming your body goes.